Geir Ottersen

Institute of Marine Research in Norway | IMR · Research Group of Oceanography

Fish stock productivity, and thereby sensitivity to harvesting, depends on physical (e.g. ocean climate) and biological (e.g. prey availability, competition and preda-tion) processes in the ecosystem. The combined impacts of such ecosystem pro-cesses and fisheries have lead to stock collapses across the world. While traditional fisheries management...

Significance It is feared that loss of old and large spawners impairs heavily fished fish stocks’ reproductive capacity and increases their sensitivity to environmental fluctuations. The Barents Sea cod is the world’s largest cod stock and has been reported to show increased temperature–recruitment associations in periods with predominantly young a...

Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year ti...

Fish populations may spawn a vast number of offspring, while only a small and highly variable fraction of a new cohort survives long enough to enter into the fisheries as recruits. It is intuitive that the size and state of the spawning stock, the adult part of the fish population, is important for recruitment. Additionally, environmental condition...

The Barents Sea ecosystem components and services are under pressure from climate change and other anthropogenic impacts. Following an Ecosystem-based management approach, multiple simultaneous pressures are addressed by using integrative strategies, but regular prioritization of key issues is needed. Identification of such priorities is typically...

The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ec...

The report is a first version of ODEMM assessments of 19 suggested valuable and vulnerable areas in Norwegian marine areas. The assessments consider 15 sectors and the respective stressors on the ecosystem components that are the basis for the valuable and vulnerable areas. In Norwegian.

The Polar Regions chapter of the Intergovernmental Panel on Climate Change's Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) provides a comprehensive assessment of climate change impacts on polar marine ecosystems and associated consequences for humans. It also includes identification of confidence for major findings based...

Marine species may respond and adapt to climate change through shifting spatial distributions, but options may be limited by the occupancy of essential habitats which are anchored in space. Limited knowledge of when spatial constraints are most likely to occur in marine fish life cycles has impeded the development of realistic distribution forecast...

This investigation commenced by constructing principal maturation schedule equations as a function of fishing mortality (F), key biophysical factors and a term attributed to fisheries-induced adaptive change (FIAC). Following the onset of industrial trawl fishery on the model stock, Northeast Arctic cod (NEAC) (1934-2020), F on immature age groups...

Reliable information about the future state of the ocean and fish stocks is necessary for informed decision-making by fisheries scientists, managers and the industry. However, decadal regional ocean climate and fish stock predictions have until now had low forecast skill. Here, we provide skilful forecasts of the biomass of cod stocks in the North...

A new dataset on the diet of Atlantic cod in the Barents Sea from the 1930s to the present day has been compiled to produce one of the largest fish diet datasets available globally. Atlantic cod is one of the most ecologically and commercially important fish species in the North Atlantic. The stock in the Barents Sea is by far the largest, as a res...

Reliable information about the future state of the ocean and fish stocks is necessary for informed decision-making by fisheries scientists, managers and the industry. However, multiyear regional ocean climate and fish stock predictions have until now had low forecast skill. Here, we provide skillful forecasts of the biomass of cod stocks in the Nor...

A new dataset on the diet of Atlantic cod in the Barents Sea from the 1930s to the present day has been compiled, to produce one of the largest fish diet datasets available globally. Atlantic cod is one of the most ecologically and commercially important fish species in the North Atlantic. The stock in the Barents Sea is by far the largest, as a re...

In high-latitude marine environments, primary producers and their consumers show seasonal peaks of abundance in response to annual light cycle, water column stability and nutrient availability. Predatory species have adapted to this pattern by synchronising life-history events such as reproduction with prey availability. However, changing temperatu...

This is an invited commentary article to the paper: A. J. Pershing et al. 2019. Challenges to natural and human communities from surprising ocean temperatures. Proc. Natl. Acad. Sci. U.S.A., 10.1073/pnas.1901084116 I recommend you read it too! Please contact me if you want our full paper. There is growing evidence indicating that variability and...

The importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density‐ and size‐dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruit...

Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year ti...

Anticipating future changes in marine social‐ecological systems (MSES) several decades into the future is essential in the context of accelerating global change. This is challenging in situations where actors do not share common understandings, practices, or visions about the future. We introduce a dedicated scenario method for the development of M...

Predicting fish stock variations on interannual to decadal time scales is one of the major issues in fisheries science and management. Although the field of marine ecological predictions is still in its infancy, it is understood that a major source of multi-year predictability resides in the ocean. Here we show the first highly skilful long-term pr...

The INTAROS project funded by H2020 for the period 2016-2021 has been established to advance the development of an integrated Arctic Observation System. INTAROS has focus on the in situ component of the observing system, where collaboration across the Pan-Arctic regions is necessary in order to make progress on the four main challenges: (1) Organis...

It has been proposed that the multiple pressures of fishing and petroleum activities impact fish stocks in synergy, as fishing-induced demographic changes in a stock may lead to increased sensitivity to detrimental effects of acute oil spills. High fishing pressure may erode the demographic structure of fish stocks, lead to less diverse spawning st...

Despite the importance both in an ecological and management context, much uncertainty remains about the underlying factors controlling spawning ground use in marine fish. Here, we investigate how spawning ground use of Northeast Arctic (NEA) haddock (Melanogrammus aeglefinus) has changed over time. By combining data from a Soviet-Russian egg survey...

Building multiple-perspective scenarios is one way to get prepared for the future. In June 2016 a workshop was organised in Sommarøya (close to Tromsø) to explore the possible futures of the Barents Sea social ecological systems using a new method for building multiple-perspective scenarios. In this poster, you can construct your own multiperspecti...

En tøff start på Barentshavstorskens liv Geir Ottersen Torskebestanden i Barentshavet er for tiden verdens største, men historisk har det vært store svingninger. Noe av dette kan tilskrives fiskeriene, men det er også mange naturlige årsaker som ligger bak. Spesielt er det stor år-til-år variasjon i hvor mange nye fisk som kommer inn i den fiskbar...

This chapter presents a review of what is known about the impacts of climate change on the biota (plankton, benthos, fish, seabirds and marine mammals) of the North Sea. Examples show how the changing North Sea environment is affecting biological processes and organisation at all scales, including the physiology, reproduction, growth, survival, beh...

We investigate how the reproductive strategy in a migratory marine fish may be influenced by spatial variations in mortality in early life stages. In particular, we examine how spawning time and location affect offspring survival and growth. A drift model for early life stages (eggs to age 1) of the Barents Sea cod (Gadus morhua) is combined with e...

Lecture at CEED Summer school 2015 on effects of climate variability and change on Arctic ecosystems + management issues

FULL TEXT NOW AVAILABLE HERE! The Barents Sea stock of Atlantic cod (Gadus morhua) is currently the world’s largest cod stock. It is also a stock for which long time-series are available and much research has been carried out. With this review, we wish to present an overview and evaluation of the knowledge on Barents Sea cod early life dynamics. Th...

Climate change is expected to have major effects on the distribution and abundance of fish. In spite of extensive research on the topic in high-latitude marine ecosystems, the mechanistic understanding of how temperature impacts recruitment and distribution of arcto-boreal fish stocks remains elusive. Exemplified by an arcto-boreal gadoid in the Ba...

Lecture for master students in biology at Univ. Oslo

The temporal and spatial dynamics of primary and secondary biomass/production in the Barents Sea since the late 1990s are examined using remote sensing data, observations and a coupled physical-biological model. Field observations of mesozooplankton biomass, and chlorophyll a data from transects (different seasons) and large-scale surveys (autumn)...

There is limited statistical support for top-down effects on plankton in oceanic ecosystems. We quantify the combined effects of key planktivorous fish, invertebrates and climate on mesozooplankton dynamics in the Barents Sea. Zooplankton biomass was measured during Russian and Norwegian surveys in April–May and June–July 1959–1990 and August–early...

Effects of variation in spawning stock and sea temperature on long-term temporal patterns in recruitment dynamics of 38 commercially harvested fish stocks in the northern North Atlantic were studied. Different statistical models were explored within a Ricker stock-recruitment framework. This includes, in order of complexity, adding a linear tempera...

Understanding the drivers (internal and external) that determine the productivity of marine ecosystems is challenging. For example, the correct estimate of recruitment is essential to estimate fish stock abundance. In this Theme Section, 5 papers explore the effect of fishing and climate on population structure across sub-Arctic ecosystems. The stu...

Environmental effects on fish populations: Some principles, some examples, and comparisons between large ecosystems from the Mediterranean to the Barents Sea The wrapping up of the IDEADOS project: Workshop on Environment, Ecosystems and Demersal Resources, and Fisheries, Palma de Mallorca from 14 to 16 November 2012

Svingninger i havmiljø og lavere trofiske nivåer (in Norwegian)

Effects of climate variability and change on sea temperature, currents, and water mass distribution are likely to affect the productivity and structure of high-latitude ecosystems. This paper focuses on the Barents Sea (BS), a productive Arcto–boreal shelf ecosystem sustaining several ecologically and economically important fish species. The water...

Nordic Climate-Fish 2nd Conference: "Latitudinal changes in marine resources, exploitation and society within the Nordic and adjacent Seas" 15-17 August 2012 in Risør, Norway  general ideas about climate effects on marine ecosystems  variations in temperature-zooplankton-North Sea cod  spatial population structure and detecting climate effects

The Norwegian Sea harbours several large pelagic fish stocks, which use the area for feeding during the summer. The period 1995–2006 had some of the highest biomass of pelagic fish feeding in the Norwegian Sea on record. Here we address the horizontal distribution and overlap between herring, blue whiting and mackerel in this period during the summ...

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Biological processes and physical oceanography are often integrated in numerical modelling of marine fish larvae, but rarely in statistical analyses of spatio-temporal observation data. Here, we examine the relative contribution of inter-annual variability in spawner distribution, advection by ocean currents, hydrography and climate in modifying ob...

Accumulating evidence shows that environmental fluctuations and exploitation jointly affect marine fish populations, and understanding their interaction is a key issue for fisheries ecology. In particular, it has been proposed that age truncation induced by fisheries exploitation may increase the population's sensitivity to climate. In this study,...

We analyse the population dynamics of Northeast Arctic cod (Gadus morhua) by applying statistical population models to 22 years of research survey data on abundance, length, and maturation. The models for abundance and individual length are selected using Akaike's information criterion (AICC). Survival of 2- to 4-year-old cod was found to be negati...

The first digital temperature atlas for the Norwegian Sea (Nordic Seas/GIN Sea) is described and examples of applications given. The atlas is intended mainly to make historical temperature values available to fisheries oceanographers, fisheries biologists, and stock assessment scientists in a structured, uniform format. It should also be of interes...

The Barents Sea stock of capelin (Mallotus villosus) has suffered three major collapses (>90% reduction) since 1985 due to recruitment failures. As capelin is a key species in the area, these population collapses have had major ecosystem consequences. By analysing data on spawner biomass and three recruitment stages (larvae, 0-group, and 1-year-old...

In order to provide better fisheries management and conservation decisions, there is a need to discern the underlying relationship between the spawning stock and recruitment of marine fishes, a relationship which is influenced by the environmental conditions. Here, we demonstrate how the environmental conditions (temperature and the food availabili...

Interactions within and between species complicate quantification of climate effects, by causing indirect, often delayed, effects of climate fluctuations and compensation of mortality. Here we identify direct and indirect climate effects by analysing unique Russian time-series data from the Norwegian Sea-Barents Sea ecosystem on the first life stag...

While documentation of climate effects on marine ecosystems has a long history, the underlying processes have often been elusive. In this paper we review some of the ecosystem responses to climate variability and discuss the possible mechanisms through which climate acts. Effects of climatological and oceanographic variables, such as temperature, s...

Climate may affect marine fish populations through many different pathways, operating at a variety of temporal and spatial scales. Climate impacts may work their way bottom up through the food web or affect higher trophic levels more directly. In this review we try to disentangle and summarize some of the current knowledge made available through th...

The Barents Sea stock of capelin (Mallotus villosus) has suffered three major collapses (>90% reduction) since 1985 due to recruitment failures. As capelin is a key species in the area, these population collapses have had major ecosystem consequences. By analysing data on spawner biomass and three recruitment stages (larvae, 0-group, and 1-year-old...

While documentation of climate effects on marine ecosystems has a long history, the underlying processes have often been elusive. In this paper we review some of the ecosystem responses to climate variability and discuss the possible mechanisms through which climate acts. Effects of climatological and oceanographic variables, such as temperature, s...

The oldest and largest individuals are disappearing from many fish stocks worldwide as a result of overexploitation. This has been suggested to impair recruitment through decreasing the reproductive capacity of the spawners and increasing the mortality rate of the offspring. By using a time series on spawners biomass by age class for Arcto-Norwegia...